Hi All,
there have been a few reports of failure to transmit while band hopping.
I believe I have got to the reason why this might be happening.
If band hopping is enabled then WSJT-X will choose the coordinated band
according this table:
#########################################################################
Coordinated hopping enables a sizable group of stations around the world
to move together from band to band, thereby maximizing the chances of
identifying open propagation paths.
Band (m) 160 80 60 40 30 20 17 15 12 10
UTC Minute 00 02 04 06 08 10 12 14 16 18
20 22 24 26 28 30 32 34 36 38
40 42 44 46 48 50 52 54 56 58
The band-selection schedule repeats starting at UTC minutes 20 and 40,
for a total of three full ten-band sequences in each hour. If the
designated band for a given time slot has not been checked as active, a
random choice is made among the active bands. The algorithm for choosing
whether to receive or transmit guarantees at least one transmission on
each active band every two hours. If all ten bands are active, up to
three transmissions may be made on a given band in a two hour period.
#########################################################################
WSJT-X allows you to select which bands you want to join the coordinated
schedule on, depending on the phase of the day (Sunrise, Day, Sunset,
Night). It also allows you to designate bands as Rx only.
Every two hours WSJT-X creates a transmit schedule based on the transmit
percentage that is set (it schedules again if the Tx percentage is
changed). This schedule is basically random but is manipulated to give
close to the expected number of transmissions per two hour period while
minimizing the number of consecutive transmit periods.
So we are running to a fixed schedule and a fixed band plan for hopping.
Before each period we first find the coordinated band, then we check if
it is enabled, if it is we will use that band next. This makes sense
because we want the herd effect of everyone who is band hopping to be on
the same band at once. If the coordinated band is set as Rx only we will
not transmit on that band. The effect of the last check is that a
transmit slot is lost and the overall number of transmits per two hours
will fall short of the expected Tx ratio. If only a few bands are
enabled for hopping and some of them are flagged as Rx only then the
overall effect on the Tx ratio could be dramatic. I believe this is
acceptable given the other constraints and given that it is better to
receive with the herd than Tx somewhere else just to maintain the Tx ratio.
The other scenario is when the coordinated band is not enabled, in this
case WSJT-X builds a list of all the bands that are enabled as a
candidate list for a random selection. This allows other bands outside
of the coordinated 10 bands to be included in band hopping as the
operator feels fit. In the case where the next period is scheduled as a
transmit period, only the bands enabled and not flagged as Rx only are
considered for a random choice so this will not reduce the overall
transmit ratio.
The above description is of r5564. Is this agreeable to everyone,
particularly the lowering of the expected Tx ratio if coordinated bands
are marked as Rx only?
73
Bill
G4WJS.
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